Gallium nitride materials include gallium nitride (GaN) and its alloys such as aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN), and aluminum indium gallium nitride (AlInGaN). These materials are semiconductor compounds that have a relatively wide, direct bandgap which permits highly energetic electronic transitions to occur. Such electronic transitions can result in gallium nitride materials having a number of attractive properties including the ability to efficiently emit visible (e.g., blue, green) or UV light, the ability to transmit signals at high frequency, and others. Accordingly, gallium nitride materials are being widely investigated in many semiconductor device applications such as transistors, field emitters, and optoelectronic devices.
Gallium nitride materials have been formed on a number of different substrates including silicon carbide (SiC), sapphire, and silicon. Silicon substrates are readily available and relatively inexpensive, and silicon processing technology has been well developed. However, forming gallium nitride materials on silicon substrates to produce semiconductor devices presents challenges which arise from differences in the lattice constant, thermal expansion, and band gap between silicon and gallium nitride.